ORAU TEAM

Dose Reconstruction

Project for NIOSH

Oak Ridge Associated Universities I Dade Moeller & Associates I MJW Corporation

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Document Title:

Calculation of Dose from Intakes of Special 

Tritium Compounds

Document Number: ORAUT-OTIB-0066

Revision: 00

Effective Date: 04/26/2007

Type of Document: OTIB

Supersedes: None

Subject Expert(s): Thomas R. LaBone

Site Expert(s): N/A

Approval: Signature on File Approval Date: 04/19/2007

James P. Griffin, Document Owner

Concurrence: Signature on File Concurrence Date: 04/23/2007

Edward F. Maher, Task 5 Manager

Concurrence: Signature on File Concurrence Date: 04/19/2007

Kate Kimpan, Project Director

Approval: Brant A. Ulsh Signature on File for Approval Date: 04/26/2007

James W. Neton, Associate Director for Science

 New Total Rewrite Revision Page Change

FOR DOCUMENTS MARKED AS A TOTAL REWRITE, REVISION, OR PAGE CHANGE, REPLACE THE PRIOR 

REVISION AND DISCARD / DESTROY ALL COPIES OF THE PRIOR REVISION.
Document No. ORAUT-OTIB-0066 Revision No. 00 Effective Date: 04/26/2007 Page 2 of 14

PUBLICATION RECORD

EFFECTIVE 

DATE

REVISION

NUMBER DESCRIPTION

04/26/2007 00 Approved new document to provide guidance for the calculation of 

best estimates of the annual organ doses for intakes of tritium bound 

to organic compounds (organically bound tritium; OBT) and tritium in 

a metal matrix (stable metal tritide; SMT). Incorporates formal 

internal and NIOSH review comments. There is no change to the 

assigned dose and no PER is required. Training required: As 

determined by the Task Manager. Initiated by Thomas R. LaBone.
Document No. ORAUT-OTIB-0066 Revision No. 00 Effective Date: 04/26/2007 Page 3 of 14

TABLE OF CONTENTS

SECTION TITLE PAGE

Acronyms and Abbreviations ...............................................................................................................4

1.0 Introduction.................................................................................................................................5

2.0 Purpose ......................................................................................................................................5

3.0 Biokinetic Models for Tritium Compounds ................................................................................... 5

4.0 Dose Calculations .......................................................................................................................8

5.0 Recommendations ....................................................................................................................10

References ........................................................................................................................................12

ATTACHMENT A, USING IMBA TO EVALUATE INTAKES OF HTO..................................................13

LIST OF TABLES

TABLE TITLE

4-1 Comparison of calculated doses for a 1-pCi acute intake of SMT...........................................

PAGE

10

LIST OF FIGURES

FIGURE TITLE

3-1 Biokinetic model for HTO .........................................................................................................

PAGE

5

3-2 Biokinetic model for SMTs........................................................................................................6

3-3 Biokinetic model for OBT..........................................................................................................7

3-4 Concentration of tritium in the urine after 1-pCi intakes of various tritium compounds.............. 8

3-5 Concentration of tritium in the urine from Figure 3-4 normalized to the same peak 

concentration ...........................................................................................................................8

4-1 Diagram from ORAUT-OTIB-0011 that shows the types of methods used to determine 

the area under an excretion curve............................................................................................9

A-1 IMBA urine bioassay model for inorganic tritium..................................................................... 14
Document No. ORAUT-OTIB-0066 Revision No. 00 Effective Date: 04/26/2007 Page 4 of 14

ACRONYMS AND ABBREVIATIONS

AMAD activity median aerodynamic diameter

d day

DOE U.S. Department of Energy

GI gastrointestinal

HTO tritiated water

ICRP International Commission on Radiological Protection

IMBA Interactive Modules for Bioassay Analysis

L liter

mCi millicurie

NIOSH National Institute for Occupational Safety and Health

OBT organically bound tritium

pCi picocurie

SAF self-absorption factor

SMT stable metal tritide

TIB technical information bulletin

U.S.C. United States Code

μCi microcurie

μm micrometer

§ section or sections
Document No. ORAUT-OTIB-0066 Revision No. 00 Effective Date: 04/26/2007 Page 5 of 14

1.0

Technical information bulletins (TIBs) are not official determinations made by the National Institute for 

Occupational Safety and Health (NIOSH) but are rather general working documents that provide 

historic background information and guidance to assist in the preparation of dose reconstructions at 

particular sites or categories of sites. They will be revised in the event additional relevant information 

is obtained. TIBs may be used to assist NIOSH staff in the completion of individual dose 

reconstructions.

INTRODUCTION

In this document the word “facility” is used as a general term for an area, building, or group of 

buildings that served a specific purpose at a site. It does not necessarily connote an “atomic weapons 

employer facility” or a “Department of Energy [DOE] facility” as defined in the Energy Employees 

Occupational Illness Compensation Program Act of 2000 [42 U.S.C. § 7384l(5) and (12)].

2.0

The purpose of this TIB is to provide guidance on how to use urine bioassay data to calculate the best 

estimates of the annual organ doses for intakes of tritium bound to organic compounds (organically 

bound tritium; OBT) and tritium in a metal matrix (stable metal tritide; SMT). 

PURPOSE

3.0

Figure 3-1 shows the biokinetic model for tritiated water (HTO) as implemented in the Interactive 

Modules for Bioassay Analysis (IMBA) software. The only difference between this model and the 

International Commission on Radiological Protection (ICRP) HTO model in Publication 67 (ICRP 

1994a) is that the IMBA model specifically includes the urinary bladder whereas the ICRP model does 

not. The water compartment has a biological half-life of 10 d, and it is assumed that 1.4/3 = 0.47 of 

the HTO in this compartment goes to urine.

BIOKINETIC MODELS FOR TRITIUM COMPOUNDS

OBT water

transfer

3% 97%

bladder other

47% 53% 

urine HTO Model

Figure 3-1. Biokinetic model for HTO.
Document No. ORAUT-OTIB-0066 Revision No. 00 Effective Date: 04/26/2007 Page 6 of 14

The OBT compartment represents tritium that is incorporated into carbon compounds and is retained 

with a half-life of 40 d as described in the ICRP carbon biokinetic model (ICRP 1994a). All of the 

tritium in this compartment is assumed to be excreted in urine. By default, IMBA does not have a 

urinary excretion function for HTO, which prevents modeling of the urinary excretion of HTO. 

Instructions on how to enable IMBA to evaluate HTO urinary excretion data are given elsewhere 

(DOE 2006).

SMTs are metals such as titanium that absorb and store tritium (i.e., H-3) atoms in the crystalline 

structure of the metal. When an SMT is inhaled, the lungs retain the material, which slowly releases 

tritium. This release of tritium occurs as the particle of the SMT dissolves and the tritium diffuses out 

of the particle. Tritium released from the SMT particle is assumed to be converted to HTO that 

subsequently behaves according to the HTO biokinetic model. The SMT biokinetic model shown in 

Figure 3-2 is therefore the HTO biokinetic model with an ICRP Publication 66 Human Respiratory 

Track Model feed compartment (ICRP 1994b). 

OBT water

transfer

3% 97%

bladder other

47% 53% 

urine

lung

Stable Metallic Tritide

Figure 3-2. Biokinetic model for SMTs.

The solubility of tritides in the lung is a function of the metal substrate (e.g., titanium versus hafnium) 

and the size and shape of the particles. Of the SMTs discussed in the literature, titanium and 

zirconium appear to be best described as type M, whereas hafnium is best described as type S 

(Mound 2004). Other tritides that consist of more reactive metals such as lithium and uranium are 
Document No. ORAUT-OTIB-0066 Revision No. 00 Effective Date: 04/26/2007 Page 7 of 14

expected to be best described as type F. [Note that lung dose from the uranium in a uranium tritide 

will be much larger than the lung dose from tritium in the uranium tritide.]

Tritium can be taken into the body already bound to carbon compounds. Such materials are referred 

to OBT compounds as opposed to the OBT compartment

Figure 3-3 shows the biokinetic model for OBT compounds as implemented in IMBA. The only 

difference between this model and the HTO model is the 50/50 split between HTO and OBT versus 

the 97/3 split for water.

in the biokinetic model. The ICRP model 

assumes that 50% of the OBT compounds taken into the body are immediately converted to HTO and 

the other 50% remain OBT.

OBT water

transfer

50% 50%

bladder other

47% 53% 

urine OBT Model

Figure 3-3. Biokinetic model for 

OBT.

Figure 3-4 shows the predicted urinary excretion curves after acute 1-pCi intakes of various tritium 

compounds, and Figure 3-5 shows these excretion curves normalized to the same peak excretion 

rate.
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1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

0 50 100 150 200 250 300 350 400

Time After Intake (days)

Tritium in Urine (pCi/liter)

OBT

HTO

Type M SMT Type S SMT

Figure 3-4. Concentration of tritium in the urine after 1-pCi intakes of various tritium 

compounds.

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 50 100 150 200 250 300 350 400

Time After Intake (days)

Tritium in Urine (pCi/liter)

HTO

OBT

Type M SMT Type S SMT

Figure 3-5. Concentration of tritium in the urine from Figure 3-4 normalized to the same 

peak concentration.

4.0

Intakes of HTO are usually evaluated using an isotopic dilution technique (HPS 1994), which is based 

on the following assumptions:

DOSE CALCULATIONS

1. HTO is metabolized like H2O.

2. The metabolic space of H2O is the 42 L of body water.
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3. The concentration of HTO in the urine is the same as the concentration of HTO in the body 

water.

These assumptions are embodied in the ICRP Publication 30 HTO biokinetic model (ICRP 1979). 

Given that these assumptions are valid, the quantity of HTO in the body at any given time is simply 

the concentration of HTO in the urine times the volume of body water, and the dose to the soft tissues 

of the body is proportional to the area under the excretion curve. 

The standard method for calculating the dose from intakes of tritiated water given in ORAUT-OTIB0011, Tritium Calculated and Missed Dose Estimates (ORAUT 2004), uses three different techniques 

to calculate the area under the excretion curve. As shown in Figure 4-1, a Type 1 tritium dose 

calculation is a linear interpolation that is performed when two urinary excretion measurements are 

less than 40 d apart. This is the classical connect-the-dots area calculation. A Type 2 tritium dose 

calculation is an exponential extrapolation from the first point to another that is performed when the 

two measurements are more than 40 d apart. A Type 2 calculation, which gives an area that is 

smaller than a Type 1 calculation, is used because it is assumed that the person did not work with 

tritium if there was no sampling for more than 40 d. Finally, a Type 3 tritium dose calculation is an 

exponential extrapolation to t = infinity that is performed to account for the “tail” after the last 

measurement.

Figure 4-1. Diagram from ORAUT-OTIB-0011 that shows the types 

of methods used to determine the area under an excretion curve.

The introduction of the OBT compartment into the ICRP HTO biokinetic model technically invalidates 

this approach because the tritium in the OBT compartment is not uniformly distributed in the bodywater space. However, the introduced error in dose is slight (about 10% is often mentioned in the 

literature) because only 3% of the HTO goes to the OBT compartment. The methodology in ORAUTOTIB-0011 compensates for this slight underestimate by adjusting the dose conversion factor upward, 

which makes the dose to systemic organs from a Type 1 calculation slightly conservative (about 5% 

high) for intakes of HTO (ORAUT 2004). Because SMTs in the lung are essentially a longer term feed 

compartment for HTO going to the systemic organs, a Type 1 calculation is also slightly conservative 

for systemic organ dose for these materials. On the other hand, a Type 1 calculation underestimates
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systemic dose by approximately 30% for intakes of OBT because half of the intake is not uniformly 

distributed in the body-water space. In practice, the error is smaller because occupational sources of 

OBT (e.g., pump oil) tend to have a significant HTO component.

Type 2 and 3 calculations make an exponential extrapolation of the urine concentration with the 

assumption of a 10-d half-life. As shown in Figure 3-5, portions of the urinary excretion curves have 

half-lives that are significantly longer than 10 d. Given a urine concentration, the dose to systemic 

organs (the area under the urinary excretion curve) from OBT and the SMTs will be underestimated 

by Type 2 and 3 calculations because they assume a 10-d half-life when the actual half-life is 

significantly longer than 10 d. As an example of a worst-case scenario, if a single urine result is 

evaluated using a Type 3 calculation (i.e., assuming it is HTO) and it is in fact from an intake of Type 

S tritide, the systemic dose for the tail

The degree to which the total systemic dose is underestimated for OBT and SMT depends on the 

fraction of the systemic dose from Type 2 and 3 calculations. For example, if the entire systemic dose 

up to the time of diagnosis is determined with Type 1 calculations, the systemic dose can be taken to 

be accurate regardless of the material. On the other hand, if most of the systemic dose is determined 

with Type 2 and 3 calculations and the material is type S SMT, the systemic dose could be 

significantly underestimated.

(not the total dose) will be underestimated by a factor of about 

6.

The dose to the lung

Table 4-1. Comparison of calculated doses for a 1-pCi acute 

intakes of tritium compounds (mrem).

from intakes of SMT can be underestimated by orders of magnitude if ORAUTOTIB-0011 calculations are used to calculate the lung dose from urinary excretion measurements

(ORAUT 2004). For example, consider the doses in Table 4-1 that result from a 1-pCi acute intake of 

the material:

ORAUT-OTIB-11

soft tissue dose

IMBA

soft tissue dose

IMBA

lung dose

Type S SMT 6.58E-10 6.30E-10 3.86E-06

Type M SMT 7.28E-09 6.93E-09 5.52E-07

HTO 7.11E-08 6.76E-08 6.76E-08

OBT 1.08E-07 1.52E-07 1.52E-07

5.0

1. In the vast majority of occupational exposures to tritium it is not possible to identify the tritium 

compound taken into the body based on the observed urinary excretion. Therefore, the 

selection of the appropriate tritium compound in an intake evaluation must usually be based on 

process knowledge of the source terms in the workplace.

RECOMMENDATIONS

2. The methodology in ORAUT-OTIB-0011 (ORAUT 2004) can be used without modification to 

calculate doses from intakes of HTO and OBT to all organs and tissues.

3. If the observed urinary excretion of tritium is deemed to be the result of intakes of SMT, 

ORAUT-OTIB-0011 (ORAUT 2004) can be used to calculate systemic dose if the majority of 

the dose is calculated with the Type 1 method. This will typically be the case if there are a 

relatively large number of urine samples over a relatively long period. On the other hand, if the 
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majority of the systemic dose is calculated with Type 2 or 3 methods, IMBA should be used to 

calculate the dose rather than ORAUT-OTIB-0011 (see next recommendation).

4. If the observed urinary excretion of tritium is deemed to be the result of intakes of SMT and the 

dose to the lung or gastrointestinal (GI) tract is needed, the urinary excretion data must be 

evaluated with IMBA in the same fashion as any other radionuclide [see Attachment A]. Note 

that the urinary excretion that results from a small intake of HTO (which gives a small lung 

dose) translates into a large SMT intake (which gives a large lung dose) if the observed 

urinary excretion is assumed to be the result of an SMT intake. This is important because the 

SMT would be expected to be associated with varying amounts of HTO in an occupational 

setting.

5. If the metal substrate of the SMT is not known, type S solubility should be assumed. However, 

fairly modest tritium urine concentrations can imply extremely large type S SMT exposures 

that might be quite implausible. For example, 1 μCi/L of tritium in the urine that is assumed to 

be the result of an intake of Type S SMT 30 d earlier implies an unencapsulated source term 

in excess of 300 mCi. This assumes that the fraction of an accidental release inhaled is 

1 × 10-6

.
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REFERENCES

DOE (U.S. Department of Energy), 2004, DOE Handbook on Radiological Control Programs for 

Special Tritium Compounds, DOE-HDBK-1184-2004, Washington, D.C., September.

DOE (U.S. Department of Energy), 2006, Guidance on Use of IMBA Software for DOE Safety 

Applications, DOE-HS-0002, Washington, D.C., December.

HPS (Health Physic Society), 1994, Internal Dosimetry Programs for Tritium Exposure, ANSI N13.14-

1994, American National Standards Institute, New York, New York.

ICRP (International Commission on Radiological Protection), 1979, Limits for the Intake of 

Radionuclides by Workers, Part 1, Publication 30, Part 1, Pergamon Press, Oxford, England.

ICRP (International Commission on Radiological Protection), 1994a, Age-Dependent Doses to 

Members of the Public from Intake of Radionuclides: Part 2 Ingestion Dose Coefficients, 

Publication 67, Oxford, England.

ICRP (International Commission on Radiological Projection), 1994b, Human Respiratory Tract Model 

for Radiological Protection, Publication 66, Oxford, England.

ICRP (International Commission on Radiological Protection), 1996, Age-dependent Doses to 

Members of the Public from Intake of Radionuclides: Part 4 Inhalation Dose Coefficients, 

Publication 71, Pergamon Press, Oxford, England.

Mound, 2004, Mound Technical Basis Document for Stable Tritiated Particulate and Organically 

Bound Compounds, MD-10516, January 24.

ORAUT (Oak Ridge Associated Universities Team), 2004, Technical Information Bulletin: Tritium 

Calculated and Missed Dose Estimates, ORAUT-OTIB-0011, Rev. 00, Oak Ridge, Tennessee, 

June 29.
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ATTACHMENT A

USING IMBA TO EVALUATE INTAKES OF HTO

Page 1 of 2

Arguably, the most common form of tritium to which workers are exposed is tritiated water, which is 

called inorganic tritium in IMBA. IMBA is not typically used to evaluate tritium urine bioassay data 

resulting from intakes of tritiated water because there are simple approaches that allow complex 

intake patterns to be readily evaluated, i.e., the method described in ORAUT-OTIB-0011 (ORAUT 

2004). However, the ORAUT-OTIB-0011 approach is frequently not applicable to urine bioassay data 

resulting from intakes of SMT. In these cases the urine data must be evaluated with IMBA in the 

same fashion as urine bioassay data from other radionuclides. The problem is that while IMBA has a 

default urine bioassay model for organic tritium, it does not offer a default urine bioassay function for 

inorganic tritium. This shortcoming can be easily rectified with the following procedure:

• Select the inorganic tritium model.

• Go to the Bioassay Model panel (shown in Figure A-1).

• Select the Urine as the bioassay function.

• Select User Defined as the mode.

• Enter the coefficients and rate constants from the following table:

A(i)

Coefficient

Lam(i)

Rate Constant

9.639E-03 1.200E+01

3.237E-02 6.931E-02

5.239E-04 1.733E-02

-4.253E-02 2.773E+00

• Enter 10-7 for the blood half-time.

Urine bioassay data in units of activity per day can now be used to directly evaluate intakes of 

inorganic tritium (SMT). 

The intake retention function calculated from this user defined urine bioassay function is the 24-hour 

incremental

IMBA files for the inhalation of Type M and Type S SMT aerosols are provided at 

urinary excretion with units of activity per day rather than per liter. This means that tritium 

urine bioassay results, which are typically in units like μCi/L, must be multiplied by 1.4 L/day to obtain 

μCi/day before being entered into IMBA.

http://imbadownloads.oraucoc.org/. 

These templates have the urine bioassay function preloaded along with the parameters for SMT 

aerosols from ICRP Publication 71 (ICRP 1996). It is recommended that these templates be used as 

the starting point for all evaluations of SMT intakes. Note that reloading the default parameters in 

these files (i.e., hitting the “ICRP DEFS LOAD” button on the IMBA main screen) will delete the HTO 

urinary excretion model.
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Figure A-1. IMBA urine bioassay model for inorganic tritium.

ATTACHMENT A

USING IMBA TO EVALUATE INTAKES OF HTO

Page 2 of 2